1. Field of the Invention
The present invention relates to a conductive paste used in electrical connection between a printed wiring board and an electronic component, or in via hole of a printed wiring board.
2. Related Art of the Invention
In the recent trend of heightened consciousness about environmental problems, used of lead in soldering is being regulated in the field of electronics mounting. It is hence an urgent matter to develop a lead-free bonding technology.
At the present, there is no lead-free solder having a performance equivalent that of the existing eutectic solder, and the conductive paste is highly expected.
In the conventional conductive paste, generally, conductive particles are disposed in insulating resin components, and after connection of electrodes, the resin is cured to keep conduction at the junction by mutual contact of particles.
However, the conventional conductive paste had the following problems.
First, noble metals such as silver, gold and palladium must be used as conductive particles, the material cost was high. The reason of using noble metals is that, in base metals such as copper and iron, insulating spontaneous oxide films formed on the metal surface are grown with the passing of the time, and the connection resistance is raised.
Second, since the metal is exposed on the surface of metal such as silver of metal particles used as conductive particles, if left over in high temperature or high humidity condition after connection, migration occurs between adjacent electrodes, and insulation failure occurs.
In the invention, accordingly, considering such problems of conductive particles using noble metals in the prior art, it is intended to present a conductive paste low in material cost and high in connection reliability and insulation reliability, its manufacturing method, and a printed wiring board using the same.
The conductive paste of the invention is composed of conductive particles having the surface of base metal particles of copper, iron, nickel, zinc, tin or the like, covered not with a spontaneous oxide film but with a very thin complex of such metal, and a binder mainly composed of insulating resin.
The manufacturing method of conductive paste of the invention is to knead the conductive particles obtained by immersing and drying metal particles in a solution containing a chelating agent, and the binder mainly composed of insulating resin.
The printed wiring board of the invention is a wiring board fabricated by using the conductive paste of the invention as a conductive paste for filling up via holes.